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The simultaneous reduction of the lattice thermal conductivity and maintenance of the electrical conductivity are great challenges for porous thermoelectric materials in achieving superior thermoel...

Designing nanoarchitectures of graphitic carbon nitride (g-CN) has been considered an effective approach to improve the photocatalytic performance, while a comprehensive understanding for the forma...

The application of thermoelectric technology is hindered by low efficiencies and high costs, demonstrating a strong demand for high-performance thermoelectric materials composed of low-cost and earth-abundant elements. PbS-based materials have attracted much attention for thermoelectric power generation due to their low-cost and earth-abundant features. However, the high lattice thermal conductivities and low electron mobilities of these materials limit their thermoelectric performance. Here, we show that we can largely reduce the lattice thermal conductivity of an n-type PbS-based material to 0.4 W m−1 K−1 through introducing zigzag nanoprecipitates with a uniform width of around 1 nm. The electron mobility was also successfully improved by reducing the effective mass through Se alloying. Finally, an extraordinary figure of merit of 1.7 at 900 K was realized in an n-type Pb0.93Sb0.05S0.5Se0.5 sample. A thermoelectric power generation module was fabricated with this n-type PbS material and our home-made high-performance p-type PbTe. It demonstrated a high conversion efficiency of 8.0% at a temperature difference of 565 K. Furthermore, a segmented module consisting of n-/p-Bi2Te3 and n-PbS/p-PbTe was fabricated, which exhibited a high conversion efficiency of 11.2% at a temperature difference of 585 K. This efficiency is the same as those of reported PbTe-based modules, and it was realized at a much lower cost. As a result, low-cost high-performance n-type PbS-based materials as a promising PbTe alternative will promote the extensive commercial application of thermoelectric power generation.

Two new inorganic metal borate derivatives, Sr5TeO2(BO3)4 and NaSr5(BO3)(SiO4)2, have been obtained through a high temperature solid reaction method. Sr5TeO2(BO3)4 crystallizes in a tetragonal space group of P4/mnc featuring a three-dimensional (3D) structure composed of a porous 3D strontium framework stabilized by the unique zero-dimensional (0D) [TeO2(BO3)4]10− anions. NaSr5(BO3)(SiO4)2 crystallizes in a monoclinic space group of P21/c with a 3D structure consisting of a splendid strontium 3D framework strengthened by isolated BO3 and SiO4 groups. The sodium cations located in the empty space of the structure. Thermal stability analyses, optical property measurements and theoretical studies of the compounds were performed. Refractive index calculations revealed that the birefringence of Sr5TeO2(BO3)4 and NaSr5(BO3)(SiO4)2 is 0.048 and 0.029, respectively, at 1064 nm.

Due to its similar crystallographic and electronic band structure to PbTe, SnTe becomes a natural alternative to PbTe for promising mid-temperature thermoelectric power generation and refrigeration. The bottleneck which restricts the thermoelectric performance of SnTe lies mainly in its relatively high lattice thermal conductivity. In this work, we found that co-doping SnTe with Cd and Cu2Te leads to “eutectoid” precipitation of CdTe- and Cu2Te-based nano-phases, which (together with Cu interstitials) can reduce the lattice thermal conductivity from ∼1.0 W m−1 K−1 for pristine SnTe to a remarkably lower level of ∼0.42 W m−1 K−1 for (Sn0.95Cd0.05Te)0.95(Cu2Te)0.05 at 823 K. With further valence band convergence by CdSn substitution and carrier concentration optimization by I-doping, we obtained a significantly enhanced figure of merit ZT of ∼1.42 at 823 K in (Sn0.95Cd0.05Te)0.93(Cu2Te)0.07-1%I. Interestingly, temperature dependent XRD measurements excluded the dynamic solution of CdTe or Cu2Te in the SnTe matrix and consequent phonon scattering reinforcement as reported. Overall, our finding of “eutectoid” precipitation of high-density CdTe/Cu2Te nano-phases, as strong scatters for mid-frequency heat-carrying phonons, might shed light on future studies on reducing lattice thermal conductivity in SnTe and related thermoelectric material systems.

In response to ever-increasing application requirements in lighting and displays, a tremendous emphasis is being placed on single-component white-light emission. Single-component inorganic borates doped with rare earth metal ions have shown prominent achievements in white-light emission. The first environmentally friendly defect-induced white-light emitting crystalline inorganic borate, Ba2 [Sn(OH)6 ][B(OH)4 ]2 , has been prepared. Additionally, it is the first borate-stannate without a Sn-O-B linkage. Notably, Ba2 [Sn(OH)6 ][B(OH)4 ]2 shows Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.42, 0.38), an ultrahigh color rendering index (CRI) of 94.1, and an appropriate correlated color temperature (CCT) of 3083 K. Such a promising material will provide a new approach in the development of white-light emitting applications.

A series of new acentric fluoroborophosphates, namely, RbBPO4F, CsBPO4F and (NH4)2BPO4F2, have been obtained by combining BO3F or BO2F2 with a PO4 tetrahedron. The structures of the isomeric RbBPO4F and CsBPO4F feature a three-dimensional diamond framework, in which a BO3F (or PO4) tetrahedron corner is shared with three PO4 (or BO3F) tetrahedra, forming 1D tunnels of eight-membered rings (MRs) along the three axial directions, which are filled with alkali cations. (NH4)2BPO4F2 exhibits a 3D supramolecular structure, in which 1D [BPO4F2]−∞ anionic chains along the a axes based on corner-sharing and alternating PO4 and BO2F2 tetrahedra are further interconnected with ammonium cations by electrostatic attractions and hydrogen bonds. RbBPO4F, CsBPO4F and (NH4)2BPO4F2 display second-harmonic generation (SHG) signals approximately 0.4, 0.6 and 0.8 times that of KH2PO4 (KDP) and exhibit short UV absorption edges (

Bistable compounds have attracted intensive interest because of their great potential to realize seamless integration of multifunctional switches in one device. However, previous studies are mainly limited to organic–inorganic hybrid compounds, which have relatively low phase-transition temperature and thermal stability. Here, we report a new pure inorganic compound CsCdPO4, which undergoes a high-temperature phase transition at 447 K. Correspondingly, CsCdPO4 simultaneously shows an interesting duple bistability of nonlinear optical and dielectric properties. Furthermore, it shows an extremely high thermal stability up to 1418 K, which is significantly higher than those of organic–inorganic bistable compounds. This work will open up a new avenue to develop multifunctional materials that remain stable even under extreme operating conditions (e.g. extremes of temperature).

Er3+/Yb3+/Eu3+: SrGdGa3O7 and Er3+/Yb3+/Ho3+: SrGdGa3O7 crystals were grown by Czochralski technology and detailed spectroscopic analyses were carried out. It was found that the spectra of Er3+/Yb3+/Eu3+: SrGdGa3O7 crystal show weaker near-infrared emission and stronger mid-infrared emission as compared with Er3+/Yb3+: SrGdGa3O7 crystal. Furthermore, the lifetime of the 4I13/2 state decreases from 10.58 ms in Er3+/Yb3+: SrGdGa3O7 crystal to 6.87 ms in Er3+/Yb3+/Eu3+: SrGdGa3O7 crystal, that is, the self-saturation for 2.7 μm laser in Er3+/Yb3+/Eu3+: SrGdGa3O7 crystal is suppressed greatly. These results indicate that the doping of Eu3+ in Er3+/Yb3+: SrGdGa3O7 crystal is beneficial to improve the 2.7 μm laser. In contrast, introducing Ho3+ in Er3+/Yb3+: SrGdGa3O7 crystal is adverse to realize Er3+-activated MIR laser operation. So Er3+/Yb3+/Eu3+: SrGdGa3O7 crystal could be a potential MIR gain media for enhanced 2.7 μm laser.

Two mixed-metal gallium iodate fluorides, namely, α- and β-Ba2 [GaF4 (IO3 )2 ](IO3 ) (1 and 2), have been designed by the aliovalent substitutions of α- and β-Ba2 [VO2 F2 (IO3 )2 ](IO3 ) (3 and 4) involving one cationic and two anionic sites. Both 1 and 2 display large second-harmonic generation responses (≈6×KH2 PO4 (KDP)), large energy band gaps (4.61 and 4.35 eV), wide transmittance ranges (≈0.27-12.5 μm), and high relevant laser-induced damage thresholds (29.7× and 28.3×AgGaS2 , respectively), which indicates that 1 and 2 are potential second-order nonlinear optical materials in the ultraviolet to mid-infrared. Our studies propose that three-site aliovalent substitution is a facile route for the discovery of good NLO materials.

Large crystal of the nonlinear optical and polar oxide Cs2TeW3O12 with a size of 20×15×4 mm3 has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808 °C and melts incongruently. It possesses a large transparent range of 0.415–5.250 μm. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30–390 °C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28 MW/cm2 with a laser wavelength of 1064 nm and pulse duration of 8 ns.

The Tm3+/Ho3+: SrGdGa3O7 single crystal was grown by the Czochralski method. The polarized absorption spectra, emission spectra and fluorescence decay curves of the crystal were measured. The crystal exhibited a broad absorption band and a broad emission band, as well as a fluorescence lifetime of 5I7 multiplet of Ho3+ ions up to 8.0 ms. End-pumped by a fiber-coupled diode laser at 808 nm, the laser operation around 2.0 µm has been realized with the a-cut and c-cut crystal samples. The maximum output power is 200 mW when a-cut crystal sample was employed.

The Sm 3+ :Sr 3 Gd(BO 3 ) 3 single crystal with dimensions of Φ 20×25 mm 3 was grown by the Czochralski method in nitrogen atmosphere. The effective segregation coefficient of Sm 3+ was measured as 0.975. The polarized absorption spectra, emission spectra and fluorescence decay curves of the crystal were measured. Based on the Judd–Ofelt theory, spectroscopic parameters of the crystal, including the oscillator intensity parameters Ω t ( t =2, 4, 6), spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes were calculated and analyzed. The crystal exhibited a broad absorption band from 390 nm to 418 nm, a broad emission band from 585 nm to 625 nm, as well as a fluorescence lifetime up to 2.04 ms. These results indicate Sm 3+ :Sr 3 Gd(BO 3 ) 3 crystal is promising for lasing in visible region.

The optical properties and dual-polarization laser operation of Yb3+:NaY(WO4)2 doped with different concentrations of Yb3+ ions have been detailedly studied in this paper. Single crystals of NaY(WO4)2 doped with 10 at%, 15 at%, 20 at%, 30 at% and 45 at% Yb3+ have been grown by the Czochralski method respectively. By comparing their room temperature polarized absorption and emission cross sections, we found that the 10 at% Yb3+:NaY(WO4) was more appropriate for laser operation. Finally the dual-polarization and dual-wavelength laser properties of 10 at% Yb3+:NaY(WO4) were measured with the output coupler of T = 3%, Rc = 75 mm. An output of 2.33 W of was achieved, which was calculated by 1000 Hz and 0.3 duty ratio pulse, and its slope efficiency is 41.3%. An output of 1.75 W of orthogonally polarized dual-wavelength laser at 1050 nm and 1055 nm was also obtained.

Absorption and emission cross-section spectra of Yb 3+ : Sr 3 Gd(BO 3 ) 3 crystal were measured. The crystal exhibited a broad emission band from 960 nm to 1125 nm. The diode-pumped continuous wave laser performance of Yb 3+ : Sr 3 Gd(BO 3 ) 3 crystal was studied for the first time and the best output power of 1.6 W with a slope efficiency of 70.3% was obtained. The simultaneous emission wavelengths could be varied from two to five with the change of absorbed pump power. An output power of 0.4 W was obtained with two-wavelength emission. Five-wavelength emission at 1060, 1064, 1066, 1071 and 1079 nm was realized with the maximum output power of 1.6 W. The redshift of the emission wavelengths was observed with the increasing of the absorbed pump power.

Ho3+ and Pr3+ ions were introduced into Er3+ : SrGdGa3O7 crystal, respectively, for enhanced 2.7 μm emissions. The effects of Ho3+ and Pr3+ on the spectroscopic properties and mutual energy transfer mechanisms were investigated. It is found that the introductions of Ho3+ and Pr3+ are helpful to achieve enhanced mid-infrared emissions and reduced near-infrared emissions. The up-conversion emission in Er3+/Ho3+ : SrGdGa3O7 crystal was stronger than that in Er3+ : SrGdGa3O7 crystal, while that in Er3+/Pr3+ : SrGdGa3O7 crystal was decreased. Introducing Ho3+ and Pr3+ depopulated the lower laser lever through energy transfer and thus reduced the fluorescence lifetime of Er3+ : 4I13/2 in Er3+/Ho3+ : SrGdGa3O7 and Er3+/Pr3+ : SrGdGa3O7 crystals to 1/2 and 1/10 of that in Er3+ : SrGdGa3O7 crystal without significantly affecting the fluorescence lifetime of the upper laser level Er3+ : 4I11/2, which greatly reduces the self-saturation problem. However, with reduced up-conversion emission and a weaker self-termination effect, Pr3+ is a more appropriate sensitizer than Ho3+ for Er3+ in this crystal. All the results imply that Er3+/Pr3+ : SrGdGa3O7 crystal could act as a potential gain media for an enhanced 2.7 μm MIR laser.